Modern printing presses are designed to operate at high speeds and are expected to produce quality images at variable press speeds, water settings, and press temperatures. There currently exists a problem of inconsistent colour control in modern printing presses due to changes in the above mentioned parameters. One potential error source is in the method of ink transference from the ink fountain roller to the high speed roller train of the press.
Modern press designs have two different types of ink ductors, either intermittent or continuous. The disadvantage of these designs is that they both suffer from inconsistent ink transfer. The ink supply is initially metered by an ink fountain blade and then transferred by way of the ductor to the high speed roller train of the press. One disadvantage of this system is that in transferring the metered ink flow rate from the ink fountain roller, a certain portion of the ink may not be transferred and will therefore be returned to the ink fountain. As such, the amount of ink transferred to the press is not known.
The net transfer of ink to the printing press is preferred to be in a state of equilibrium for most printing applications. This equilibrium is easily disturbed by changes in variables such as press speed, water setting, and temperature of the high speed roller train. After such disturbances, a new equilibrium is established that results in a new and usually different ink transfer rate to the printing press. The disadvantage of this is that if the metered ink flow rate supplied by the fountain blade is constant, the ink transfer rate to the printing press must change with the change in variables. This variability in ink transfer rate could eventually result in an undesired solid colour density change of the printed material produced by the printing press.
Another disadvantage with present printing press systems is that adjustments have to be made to the ink flow settings when the press runs at different speeds. The correct setting of ink keys and ink fountain roller settings to provide a desired ink transfer rate are not always predictable.
It is an object of the present invention to obviate or mitigate the above mentioned disadvantages.